Divider/combiners are known in the art for dividing or combining electrical signals. For example, an RF signal generator may produce a radio frequency signal at a power level on the order of 25 watts and it may be desired that the signal be boosted in power to a level on the order of 1 kw. Solid state power amplifiers may be employed However, there are limitations in the power handling capability of such amplifiers. It is for this reason that it is common to divide the RF signal and apply the divided signals to several paths, each of which includes an RF power amplifier operating at a level of, for example, 1 kw. The amplified RF signals are then combined and supplied to an RF load. The signal dividers and combiners are frequently constructed in the same manner and, hence, are referred to as a divider/combiner.
Divider/combiners capable of performing the function noted above are known in the art. For example, the M. Dydyk U.S. Pat. No. 4,367,445 describes, in its introduction, a divider/combiner known as the Wilkinson device. That device has three ports including a common input/output port and a pair of output/input ports. The output/input ports are electrically connected to the common input/output port by transmission lines wherein each path is of the same electrical length.
It is further known in the prior art to provide N-way divider/combiners based somewhat on the Wilkinson device and which are employed for in-phase operation. As an N-way in-phase divider, an RF signal is supplied to an input port and is split and the split RF signals arrive at the output ports in phase with each other.
It has been known in the prior art to employ such an N-way in-phase divider for supplying RF signals, to be boosted in power, to N RF power amplifiers with the outputs of the power amplifiers being supplied to an N-way in-phase combiner for combining the signals. In this example, the N output ports of the divider are connected to respective inputs of N power amplifiers. Normally, these power amplifiers are designed to operate in a particular system (characteristic) impedance, such as 50 ohms. Any impedance other than this particular impedance will result in a mismatch at the divider output ports. If each has the same mismatch, this will be reflected back from the input of the amplifier through the divider to the common input which is connected to a common RF signal source. Since the transmission lines of the divider are of the same electrical length, the reflected signals will arrive back in-phase with each other and the mismatch from each output port will be additive when the signals arrive at the common input port. This will detract from the efficiency of performance of the system, such as loss of power while generating more heat. A similar situation exists in the opposite direction when employing such circuitry as a combiner.
A quadrature combiner is an N-way combiner, wherein N=2, and having 90.degree. phase shift between combined ports. This structure is commonly used for cancellation of uniform mismatches at the combined ports, providing the system (characteristic) impedance.
Given a system comprised of an amplifier and a mismatched load, where the amplifier has a mismatch at its output port, there exists a variation in delivered power to the load as the phase of the load mismatch is varied. This is commonly known as mismatch uncertainty, and is due to the interaction between amplifier output impedance (mismatch) and the impedance (mismatch) of the load being driven.
This same effect occurs when outputs of identical amplifiers are combined in-phase, where the variable phase mismatch is placed on the common port. Each amplifier drives an equivalent impedance (magnitude and phase), thus the "mismatch uncertainty" of delivered power is cumulative.
"Quadrature" combining (using 90.degree. combiners) solves the problem for N=2, but for N&gt;2 provides no additional advantage in terms of reduced mismatch uncertainty.
The invention herein provides for different electrical lengths to each of N ports (where N is an even integer, greater than two), from the common port. This results in each of N amplifiers driving an impedance which is shifted in phase by 360/N degrees from "adjacent" amplifiers. Thus, while each amplifier exhibits the same "mismatch uncertainty" as before, the uncertainty of each amplifier is staggered in phase with respect to the other amplifiers. Thus, while one amplifier is delivering its maximum power, another amplifier is delivering its minimum, and all remaining amplifiers are delivering power between these two extremes. The net effect is that the combined power from all amplifiers is much more independent of phase, remaining relatively constant as the phase of the load mismatch is varied. This reduction in power variation continues to improve as N is increased beyond N=4.
Simultaneously, this invention incorporates prior art "quadrature" combiners which provide compensation for uniform impedance mismatches at the N non-common ports. This feature is useful for combining multiple components which exhibit similar impedance mismatches.